MUNICH (Reuters) - German authorities on Friday returned 500 historical books including original works by Renaissance scientists Galileo Galilei and Nicolaus Copernicus, stolen from Italian libraries three years ago, to Naples prosecutors.

Most of the books, worth around 2.5 million euros, were stolen from the Girolamini library in Naples, according to Italian prosecutors. German authorities seized them in a Munich auction house at the Italians' request.

The former director of the library, Massimo De Caro, was convicted of stealing the books and served a jail sentence before being put under house arrest.

"As director his role was to do all he could to protect and preserve the books. However, he reversed his function. By taking advantage of his position, he was able to remove books," said prosecutor Vincenzo Piscitelli, in Munich to collect the works.

"He deactivated the security alarm systems, carried out his activities during night hours or during the holidays when library staff were not there. He was alone, he had the keys, everyone knew he was the director. Therefore he was able to work in complete freedom," he added.

Prosecutors are still trying to discover how many books disappeared in total from the library, which is one of Italy's oldest and richest.